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Synthesis

Rhodium-Catalyzed Route Builds Three-Membered Nitrogen Rings From Olefins

Chemists synthesize common building block found in nature and in medicine in one step

by Carmen Drahl
January 6, 2014 | APPEARED IN VOLUME 92, ISSUE 1

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The hindered tetrasubstituted olefin shown isn’t compatible with most aziridination reactions, but in the new method it works in 70% yield.
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The hindered tetrasubstituted olefin shown isn’t compatible with most aziridination reactions, but in the new method it works in 70% yield.

When it comes to synthetic building blocks, the triangular nitrogen heterocycle known as aziridine has plenty going for it. Because of its geometry, aziridine’s strained ring makes it a ready participant in reactions that build complex molecules. For example, the ring appears in bioactive natural products, including chemotherapy drug mitomycin C. Yet with few exceptions, aziridination methods require a protecting group on the nitrogen, which can be tough to remove while keeping the aziridine ring intact. A multilab team has now reported a one-step method that transforms olefins into N–H and N–CH3 aziridines under mild conditions (Science 2013, DOI: 10.1126/science.1245727). László Kürti and John R. Falck of the University of Texas Southwestern Medical Center and Daniel H. Ess of Brigham Young University had previously explored reactions using the aminating agent O-(2,4-dinitro­phenyl)hydroxylamine, which they now use for aziridination. They also found that a rhodium catalyst and 2,2,2-trifluoroethanol solvent are essential. Their approach works on hindered olefins and doesn’t disturb sensitive functional groups. The method isn’t enantioselective yet, Kürti says, but the team is using the Ess lab’s density functional theory calculations to hunt for the right catalyst for that job.

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